1. Field of the Invention
This invention relates to a screen apparatus for paper making which is used for production and treatment of regenerated pulp, treatment of damaged paper, or treatment of waste paper such as newspapers, magazines or the like, and more particularly to a screen apparatus for paper making which is adapted to treat a paper feedstock containing unmacerated fiber pieces to carry out maceration and recovery of the unmacerated fiber pieces and discharge tailings to an exterior of the paper making system.
2. Description of the Related Art
In a paper making process such as the production and treatment of regenerated pulp, treatment of damaged paper, treatment of waste paper or the like, as shown in FIG. 1, a paper feedstock macerated in a pulper is subject to screening using a primary round hole screen and a slit screen and then subjected to dehydration by means of a dehydrator. Tailings obtained by screening the feedstock through the primary round hole screen contain a large amount of unmacerated fiber pieces, therefore, generally the tailings are introduced into a macerator for further maceration and then stored in a chest. Then, the resultant macerated tailings are fed to a secondary round hole screen by means of a pump, so that the available or effective fiber content is recovered from the macerated tailings. Thereafter, the macerated tailings from which the effective fiber content has been separated are fed to a final screen to recover the additional effective fiber content still contained in the tailings and carry out maceration and recovery of unmacerated fiber pieces remaining in the tailings, as well as to discharge any impurity or residue to an exterior of the paper making system. Unfortunately, the residue discharged through the final screen has a concentration as low as 1 to 3% and contains a large amount of water, therefore it is required to further dehydrate the residue before the subsequent treatment and disposal thereof.
Also, in order to promote maceration and recovery of the unmacerated fiber pieces contained in the tailings obtained by screening using the primary round hole screen, it is required to arrange attachment equipment such as the above-described macerator, chest, pump, secondary round hole screen and final screen, as well as valves, pipings and the like, so that facilities for paper making become highly complicated and enlarged and the paper making operation becomes troublesome. Further, as described above, the residue obtained by screening using the final screen contains lots of water, resulting in the handling and treatment thereof being highly troublesome.